Improving the efficiency of a lab-on-a-chip total alkalinity analyzer via Dean flow–driven mixing

Autonomous chemical analyzers capable of high-frequency in situ measurements can greatly enhance ocean observations, supporting biogeochemical and climate research. Here, an optimized Lab-on-a-Chip (LoC) total alkalinity (TA) analyzer is presented, integrating a compact Dean flow micromixer into a microfluidic closed-cell titration and spectrophotometric system for autonomous seawater analysis. Previous studies of Dean flow mixing have largely focused on micromixer design and mixing performance using numerical simulations or model fluids (e.g., dyes). In contrast, this work evaluates micromixer operation under analytical constraints directly relevant to chemical sensing, including on-chip multipoint titration, optical absorbance fidelity, and transport-limited dispersion effects. Secondary Dean vortices and mixing efficiency were characterized numerically and experimentally over a wide range of flow rates. Taylor dispersion was quantified to establish a lower bound on usable injection volumes, ensuring optical measurements remain accurate at reduced volumes. The optimized system consumes, on average, ~32 μL of titrant and ~ 159 μL of sample per titration point and completes a full TA measurement with nine titration points in under 10 min. This represents a 4.5-fold reduction in reagent consumption and 2-fold decrease in measurement time relative to the previous design. TA performance was validated using standard solutions spanning 1700–2300 μmol/kg, achieving an accuracy of